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OK, this part was brilliant: "To avoid this problem, the team divided their 100-milliwatt laser into eight beams. Each beam travels along a slightly different

OK, this part was brilliant: "To avoid this problem, the team divided their 100-milliwatt laser into eight beams. Each beam travels along a slightly different path through the turbulent atmosphere and thus receives a different random phase perturbation. Counterintuitively, this incoherent illumination makes the interference effects observable. When I first started studying optical engineering, my teacher had worked on the first under-the-RADAR guidance system for bombers. He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane. He taught us about the nominal amount of turbulence in the atmosphere, and that it limited space-based cameras to about half a foot resolution - a limit he said couldn't be broken. Therefore, license plates would never be readable from space... Before I was out of grad school, they had broken it with laser techniques on nearby targets. Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image. A lot of processing (for that day), but it could be done back on Earth. As you can see from the test images, the 8 lasers aren't enough to perfectly smooth out the noise. The noise is probably square-root-8 improved, so resolution should improve by a factor of not quite 3. Move those lasers slightly and repeat 12 times; you've improved resolution by 10. This is easy to do quickly; you should be able to read fine print held by a car passenger on the highway.

perihelions 2y ago
- "Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image" That's also how some adaptive optics work in astronomy, https://en.wikipedia.org/wiki/Laser_guide_star https://en.wikipedia.org/wiki/Laser_guide_star
- embwbam 2y ago
  The adaptive optics system for the DKIST solar telescope actually deforms each point of the mirror at 60Hz or something to do wavefront correction!
  - pfdietz 2y ago
    Big telescopes have to actively deform the primary mirror anyway, just to keep it in proper shape as it moves around under gravity loads.
kevmo314 2y ago
That's how night mode works on Pixel phones, right? I believe it takes a few images in rapid succession and took advantage of the noise being random which meant a high quality image under a noisy sensor with some signal processing.
- Calwestjobs 2y ago
  some phones shine IR floodlight, too.
- picture 2y ago
  Integrating over a longer time to get more accurate light measurements of the a scene has been a principal feature of photography. You need to slow down the shutter and open up the aperture in dark conditions. Combining multiple exposures is not significantly different from a single longer exposure, except the key innovation of combining motion data and digital image stabilization which allows smartphones to approximate longer exposures without the need of a tripod.
  - tonyarkles 2y ago
    I agree with you wholeheartedly and just want to add one more aspect to this: it also allows you do handle the case where the subject is moving slowly relative to the camera. Easy example is taking long exposures of the moon from a tripod. If you just open the shutter for 30 seconds the moon itself is going to move enough to cause motion blur; if instead you take a series of much faster photos and use image processing techniques to stack the subject (instead of just naively stacking all of the pixels 1:1) you can get much better results.
    - magicalhippo 2y ago
      For bright stuff like the moon, it's my understanding the best way is take really high-speed video, hundreds of frames per second, then pick out the frames which has the least amount of atmospheric distortion and stack those. So not only can you compensate for unwanted motion of the camera rig, but also for external factors like the atmosphere. For faint deep-sky objects, IIRC you really do want long exposures, to overcome sensor noise. At least the comparisons I've seen using same total integration time, a few long exposures had much more detail and color compared to lots of short exposures. That said, lots of short exposures might be all you can do if you're limited by equipment or such, and is certainly way better than nothing.
deleted 2y ago
[deleted]
hammock 2y ago
>He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane. You ought to read Tom Wolfe’s “the right stuff” asap if you haven’t already
- bookofjoe 2y ago
  And watch this video of Neil Armstrong nearly getting killed when his test flight of a lunar lander trainer (on Earth) crashed and burned: https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV
dekhn 2y ago
We are in the middle of a renaissance of image processing across a wide range of fields. Many of the previous limits are being smashed by using new materials and algorithms. See https://en.wikipedia.org/wiki/Fourier_ptychography https://en.wikipedia.org/wiki/Fourier_ptychography for an example
- nereye 2y ago
  Applied Science YT channel has an interesting video showing this at work: Dramatically improve microscope resolution with an LED array and Fourier Ptychography https://www.youtube.com/watch?v=9KJLWwbs_cQ https://www.youtube.com/watch?v=9KJLWwbs_cQ
  - cenamus 2y ago
    Damn, somehow missed this video as a long time subscriber.
- globnomulous 2y ago
  Wow, I had no idea. I know nothing about the field, so maybe someone better educated can answer my innocent, probably naive question: my instincts tell me that any technology that makes humans better at manipulating or interpreting light has vast potential to alter our lives. Is that right?
quantadev 2y ago
So what's the summary of how this works? I don't think it was explained well, and I'm fairly up to speed with the physics of photons etc. Is it that the multiple lasers are able to destructively interfere with each other so that they cancel out the noise from each other since the noise will be the same in all of them? That's tricky because if the photons are phase shifted to cancel out the noise that seems like the ENTIRE laser signal would be cancelled out too. Maybe this is what's happening, and the only thing "left over" is the signal from the source (what's being measured)?

perihelions 2y ago

- "Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image" That's also how some adaptive optics work in astronomy, https://en.wikipedia.org/wiki/Laser_guide_star https://en.wikipedia.org/wiki/Laser_guide_star

embwbam 2y ago
The adaptive optics system for the DKIST solar telescope actually deforms each point of the mirror at 60Hz or something to do wavefront correction!
- pfdietz 2y ago
  Big telescopes have to actively deform the primary mirror anyway, just to keep it in proper shape as it moves around under gravity loads.

kevmo314 2y ago

That's how night mode works on Pixel phones, right? I believe it takes a few images in rapid succession and took advantage of the noise being random which meant a high quality image under a noisy sensor with some signal processing.

Calwestjobs 2y ago
some phones shine IR floodlight, too.
picture 2y ago
Integrating over a longer time to get more accurate light measurements of the a scene has been a principal feature of photography. You need to slow down the shutter and open up the aperture in dark conditions. Combining multiple exposures is not significantly different from a single longer exposure, except the key innovation of combining motion data and digital image stabilization which allows smartphones to approximate longer exposures without the need of a tripod.
- tonyarkles 2y ago
  I agree with you wholeheartedly and just want to add one more aspect to this: it also allows you do handle the case where the subject is moving slowly relative to the camera. Easy example is taking long exposures of the moon from a tripod. If you just open the shutter for 30 seconds the moon itself is going to move enough to cause motion blur; if instead you take a series of much faster photos and use image processing techniques to stack the subject (instead of just naively stacking all of the pixels 1:1) you can get much better results.
  - magicalhippo 2y ago
    For bright stuff like the moon, it's my understanding the best way is take really high-speed video, hundreds of frames per second, then pick out the frames which has the least amount of atmospheric distortion and stack those. So not only can you compensate for unwanted motion of the camera rig, but also for external factors like the atmosphere. For faint deep-sky objects, IIRC you really do want long exposures, to overcome sensor noise. At least the comparisons I've seen using same total integration time, a few long exposures had much more detail and color compared to lots of short exposures. That said, lots of short exposures might be all you can do if you're limited by equipment or such, and is certainly way better than nothing.

deleted 2y ago

[deleted]

hammock 2y ago

>He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane. You ought to read Tom Wolfe’s “the right stuff” asap if you haven’t already

bookofjoe 2y ago
And watch this video of Neil Armstrong nearly getting killed when his test flight of a lunar lander trainer (on Earth) crashed and burned: https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV

dekhn 2y ago

We are in the middle of a renaissance of image processing across a wide range of fields. Many of the previous limits are being smashed by using new materials and algorithms. See https://en.wikipedia.org/wiki/Fourier_ptychography https://en.wikipedia.org/wiki/Fourier_ptychography for an example

nereye 2y ago
Applied Science YT channel has an interesting video showing this at work: Dramatically improve microscope resolution with an LED array and Fourier Ptychography https://www.youtube.com/watch?v=9KJLWwbs_cQ https://www.youtube.com/watch?v=9KJLWwbs_cQ
- cenamus 2y ago
  Damn, somehow missed this video as a long time subscriber.
globnomulous 2y ago
Wow, I had no idea. I know nothing about the field, so maybe someone better educated can answer my innocent, probably naive question: my instincts tell me that any technology that makes humans better at manipulating or interpreting light has vast potential to alter our lives. Is that right?

quantadev 2y ago

So what's the summary of how this works? I don't think it was explained well, and I'm fairly up to speed with the physics of photons etc. Is it that the multiple lasers are able to destructively interfere with each other so that they cancel out the noise from each other since the noise will be the same in all of them? That's tricky because if the photons are phase shifted to cancel out the noise that seems like the ENTIRE laser signal would be cancelled out too. Maybe this is what's happening, and the only thing "left over" is the signal from the source (what's being measured)?